This invention relates to an induction system for an engine, and more particularly to an improved induction system for a multi-valve internal combustion engine.
It has been recognized that there are certain advantages in promoting turbulence in the combustion chamber, particularly under at least some running conditions and loads. One type of turbulence which is generated in the combustion chamber, generally through the use of the induction system, is "swirl." Swirl is a rotary motion occurring about an axis that is either coincident with or parallel to the cylinder bore axis. Another type of motion, which has been proven to be more effective under at least some running conditions, is called "tumble." Tumble is also a swirling motion in the combustion chamber, but tumble rotates about an axis that is disposed transversely to the cylinder bore axis. That is, the intake charge is delivered into the cylinder so as to flow toward one side thereof, impinge upon the cylinder, be directed downwardly to strike the head of the piston, and be redirected back toward the other side of the cylinder so as to generate this tumbling motion. Like swirl, tumble is generated primarily in the configuration of the induction system.
In addition to the desirability of introducing some motion to the intake charge, the induction system also should be capable of introducing adequate air flow for maximum engine output. This gives rise to the use of multiple intake valves, and although two valves per cylinder are common, three intake valves per cylinder may be more desirable under a number of circumstances.
However, with the use of three valves per cylinder, the valve placement frequently is such that some of the intake valves can be used to create a tumble action, but the remaining intake valves may cause a reverse tumble action that opposes the tumble from the first valve or valves. Although this reverse action may be desirable for controlling the speed of tumble, it is also important to ensure that the desired rate of tumble is accomplished.
One advantage of tumble motion is that the tumble action is accelerated as the piston approaches top dead center. That is, the path which the air must flow when completing its circle decreases as the piston approaches top dead center. As a result, the rate of tumble increases.
It is, however, also important to ensure that the tumble is not excessive, because too much tumble can produce results that are not desirable. It has been found that the best performance, under at least some running conditions, can be accomplished when the center or axis about which the tumble occurs is the center of the volume of the combustion chamber when the piston is traveling at a maximum speed.
It is, therefore, a principal object of this invention to provide an improved induction system for an engine for generating tumble.
It is another object of this invention to provide an improved induction system for a multi-valve engine wherein the desired degree of tumble can be obtained.
It is a still further object of this invention to provide an improved induction system for an internal combustion engine wherein the optimum tumble condition can be achieved, even when using three intake valves per cylinder.